This invention relates to a probing apparatus and, more particularly, to a wafer prober for use in the examination of electrical characteristics of semiconductor devices formed on a wafer, during the manufacture of such semiconductor devices.
Usually in the field of manufacture of semiconductor devices such as integrated circuits (ICs), and during one of the final stages of the manufacture, the electrical characteristics of semiconductor devices, called IC chips, formed on a silicon wafer or the like are examined. Such examination is normally effected prior to cutting the wafer to divide the same into respective IC chips. For the sake of such examination, an integrated-circuit tester, called an IC tester, and a probing apparatus, called a wafer prober, are used. The examination itself of the electrical characteristics of each of the IC chips is carried out actually by the IC tester, and the wafer prober is used in order to establish an electrical connection between the IC tester and each of the IC chips on the wafer. An example of a known type wafer prober is shown in FIG. 7.
The water prober shown in FIG. 7 includes a sender carrier 1 which contains a plurality of wafers each having formed thereon a number of IC chips. For the examination, a first one of such wafers, to be tested, is fed to a wafer stage 3 of the probing apparatus. The wafer stage is movable in the directions of X, Y, Z and .theta. (as labelled in FIG. 7). On the other hand, a probe card 7 associated with the wafer 4 to be tested is introduced into the probing apparatus and then is held by a holder 11 for rotational displacement in an X-Y plane. Although not shown in this Figure, the probe card 7 has mounted thereon a plurality of probe needles with tips. The number of the probe needles and the positions of the needle tips correspond respectively to the number and the locations of bonding pads of each IC chip on the wafer. The bonding pad is the area defined on the IC chip to which a bonding wire is to be connected at a later stage during the manufacture of the semiconductor devices.
The probe card 7 and the wafer stage 3, carrying the wafer 4, are relatively displaced so that the tips of the probe needles are aligned with the bonding pads of one of the IC chips which is now going to be examined. Subsequently, the wafer stage is moved upwardly in the Z direction until the tips of the probe needles contact the bonding pads of the IC chip, respectively. By thus bringing the needle tips into contact with the bonding pads, the IC chip is electrically connected to an unshown IC tester so that the examination of the electrical characteristics of the IC chip is carried out.
Upon completion of the examination, the wafer stage 3 is moved downwardly in the Z direction and then is moved stepwisely in the X and/or Y direction relative to the probe card so that a second IC chip is examined in a similar manner. This is repeated until all the remaining IC chips are examined. If the examination results show that the IC chip is defective, an unshown inker is used to mark such IC chip. When the examination relative to all the IC chips on the wafer 4 is completed, the wafer 4 is unloaded from the wafer stage 3 and is fed into a receiving carrier 9.
Thereafter, a second wafer is introduced into the probing apparatus and similar examination operations are carried out relative to the second wafer.
If the examination is to be made relative to different IC chips having different patterns (and thus having different geometrical arrangements of bonding pads), separate probe cards having different arrangements of probe needles are interchangeably used.
In any event, in order that the probe needles of the probe card are brought into correct contact with the bonding pads of the IC chip, respectively, an accurate alignment must be achieved between the probe card and the wafer (i.e. between the tips of the probe needles and the bonding pads) after they are introduced into the probing apparatus.
The alignment operation in the known type probing apparatus will now be described. Usually, the alignment of the wafer is effected through two steps, prealignment (coarse alignment) and final alignment (fine alignment).
The wafer prealignment is a step for coarsely positioning the wafer relative to the probing apparatus or the probe card. In FIG. 7 example, the wafer prealignment is carried out at a prealignment station 2 by mechanical positioning. By the wafer prealignment, the wafer is coarsely positioned so that its orientation flat extends in a desired direction relative to the probing apparatus.
After the wafer prealignment, the final or fine alignment of the wafer relative to the probe card is effected. As for the first wafer 4, the same is moved manually so that a predetermined one of the IC chips on the first wafer 4 is located under the probe needles. Subsequently, while observing the tips of the probe needles and the bonding pads of the IC chip through a microscope (alignment scope) 10, the probe card 7 is manually displaced in the rotational direction to remove the positional deviation in the rotational direction between the probe card 7 and the wafer 4 (i.e. between the tips of the probe needles and the bonding pads of the IC chip). By this, the positioning of the probe card 7 is completed. Then, while continuing the naked-eye observation, the wafer stage 3 is manually displaced minutely in the X and Y directions to accurately align the bonding pads of the IC chip and the tips of the probe needles. When this is achieved, the alignment of the first wafer 4 is completed.
On the other hand, the fine alignment of a second wafer, a third wafer, etc. can be effected automatically. For this purpose, the wafer prober shown in FIG. 7 is provided with an automatic alignment sensor 5 which is adapted to detect accurately the position of the wafer held by the wafer stage 3, through image processing (pattern matching) with the use of a TV camera or through a laser beam scanning system.
If the fine alignment relative to the second wafer, the third wafer, etc. is to be made automatically through the image processing, the following operations are carried out just after the completion of the fine alignment of the first wafer 4. That is, the first wafer 4, as to which the fine alignment is finished, is moved so that a predetermined area on the first wafer 4 is located at a position under the TV camera 5 provided for the sake of the image processing. By doing so, the image of the pattern in the predetermined area on the wafer 4 is picked up and the pattern is displayed in a cathode ray tube connected to the TV camera 5. Subsequently, of the pattern displayed, a desired or predetermined portion is selected and registered as a template. This template is used as a reference for detecting the position of each of the second wafer, the third wafer, etc. during the automatic fine alignment of these wafers.
Similarly, in the case of the automatic alignment through the laser beam scanning system, the first wafer as to which fine alignment has been achieved is moved by the wafer stage 3 so that a predetermined area on the first wafer is located under the sensor 5. By scanning the predetermined area with the laser beam, a reference signal train is obtained.
In any case, the fine alignment of the second wafer, the third wafer, etc. is accomplished with the predetermined area of the wafer being moved to a position under the sensor 5.
Denoted by a numeral 6 in FIG. 7 is a height sensor which is adapted to detect the height of the wafer surface to thereby control the amount of upward displacement, in the Z direction, of the wafer stage 3 during the probing operation. The height sensor 6 is used also to detect the edge, the center, etc. of the wafer. Denoted by a numeral 8 is an operation panel with which the operator instructs various operations of the probing apparatus.